Compact drive

ABSTRACT

The invention concerns a compact drive with an electric motor, a frequency converter and a gear. Such a drive should be made in the most compact way possible. For this purpose frequency converter is arranged at one front end of the motor and the gear is arranged at the other front end of the motor.

The invention concerns a compact drive with an electric motor, afrequency converter and a gear.

The motor is an alternating or a three-pulse current motor. Alsopermanent magnet motors, switched reluctance motors or direct currentmotors can be used. The motor is supplied by the frequency converter anddelivers its mechanical output via the gear.

The purpose of the invention is to make a compact drive as compact aspossible.

In a compact drive as mentioned in the introduction, this is solved inthat the frequency converter is arranged at one front end of the motorand the gear is arranged at the other front end of the motor.

This embodiment involves several advantages: Firstly, there is a clearseparation between the electrical supply taking place on one side of themotor, and the mechanical power output taking place on the other side ofthe motor. The length of the drive will increase somewhat due to thismeasure. However, it can be ensured that both gear and frequencyconverter have substantially the same cross-sectional area as the motor,so that laterally fitted parts can be avoided. Secondly, the motor willneed fewer housing parts, as the front covers of the motor are replacedby the frequency converter and the gear, respectively. Thus also theaxial extension of the drive caused by the gear and the frequencyconverter can be kept within reasonable limits. Further, the productionof such a compact drive is more simple. Normally, the stator winding hasits connections in the area of a front end of the motor. When thefrequency converter is connected here, the cables are kept short. Theconnections are correspondingly easier to wire and connect. Here, theterms “frequency converter” and “gear” are used as common terms. Thefrequency converter can be made so that it converts a direct currentinto a one- or multi-phase alternating current, or converts a one- ormulti-phase alternating current into a direct current or an alternatingcurrent with a different frequency. The gear converts the mechanicalenergy defined by the speed and torque of the motor shaft to a differentform, that is, a different speed or a different torque, or even to adifferent sort, for instance hydraulic or pneumatic pressures. In thiscase the gear is a pump.

In a preferred embodiment it is provided that the frequency converterhas a frequency converter housing with a bottom plate of a heatconductive material, which bottom plate is fitted on the stator of themotor. The housing of the frequency converter can therefore be made withreduced stability. The actual stability is obtained in that the housingof the frequency converter is fitted on the stator of the motor.However, the stator of the motor is an extremely stable part, andcorrespondingly, it also stabilises the housing of the frequencyconverter via the bottom plate. Usually, the frequency converter is thepart of the compact drive producing most heat. This is caused byelectrical losses during the frequency conversion, that is, theconversion of a d.c. to an a.c. or the conversion of an alternatingvoltage. Making at least the bottom plate of a heat conductive materialcauses that the heat can be distributed and then given off to thesurroundings via this bottom plate. In many cases an additional coolingwill not be required.

It is also preferred that the gear has a baseplate of a heat conductivematerial, which baseplate is fitted on the stator of the motor. Thefacts applying for the bottom plate of the frequency converter alsoapply for this baseplate. The baseplate is mechanically stabilised bythe stator of the motor, which is the mechanically most stable part ofthe compact drive. The heat produced can be distributed and then givenoff to the surroundings via this baseplate. The dimensions of the gearhousing can be correspondingly weaker, as the motor serves asstabiliser.

Preferably, the bottom plate and/or the baseplate are in heat-conductiveconnection with the stator. The heat from the frequency converter or thegear, respectively, is no longer just given off to the surroundings.Through the bottom plate and/or the baseplate it can be led into thestator. The stator, which normally has a larger metal mass than thefrequency converter, can absorb this heat. Additionally, it also has alarger heat-emitting surface, via which the heat can be given off to thesurroundings. This causes that practically no additional coolingmeasures, such as forced ventilation etc., must be taken. Still, athermally stable operation is obtained in spite of the compactdimensions.

In a particularly preferred embodiment it is provided that the bottomplate and/or the base plate have a bearing housing for the rotor of themotor. Thus, the rotor is carried in the bottom plate of the frequencyconverter and/or the baseplate of the gear, respectively. This saves anadditional bearing in the gear. The gear “shares” a bearing with themotor. In connection with the frequency converter this has theadditional advantage that also via the rotor bearing there is a certainheat emission. Of course, this heat emission is limited, as only alimited heat flow can be transported via the bearing. In total, anadditional equalisation of the temperature distribution and a reductionof the peak temperatures can be observed. This construction alsofacilitates the assembling. The compact drive can be assembled byplacing the frequency converter and the gear from both sides on thestator. Thus, the rotor is also automatically carried in the stator.

It is particularly preferred that the bottom plate and/or the baseplatehave a circumferential centring projection in the area of itscircumferential edges next to the motor, which projection surrounds thestator. This provides that the bottom plate or the baseplate,respectively, are fitted with a predetermined orientation in relation tothe stator, so that also the bearing housing for admission of thebearing is oriented concentrically in relation to the stator bore. Nofurther orientation measures are thus required. This facilitates themounting considerably. Additionally, this measure secures against alateral displacement of the frequency converter or the gear,respectively, in relation to the motor. The circumferential centringprojection can also be interrupted, as long as it secures that theconcentric orientation of the frequency converter or the gear,respectively, in relation to the motor is maintained.

It is particularly preferred that the bottom plate and/or the baseplateare made of aluminium. On the one hand aluminium has the desired heatconductivity and on the other hand it has the required mechanicalstability for admission of the bearing housing. These advantages arecombined with a low weight, so that the compact drive can not only bekept small with regard to its dimensions, but also with regard to itsweight.

Advantageously, the frequency converter and the gear are clampedtogether, thus holding the motor between them. Thus, no additionalfixing opportunities are required on the motor. The motor is heldbetween the frequency converter and the gear by means of clampingforces. Fixing opportunities are thus only required on the frequencyconverter and the gear. This facilitates both the production of theindividual parts and the assembling of frequency converter, motor andgear.

It is also advantageous that the circumference of the stator hasimmediate connection with the surrounding atmosphere. In thisconnection, a protective shield, that is, a housing, for the motor isabandoned. The circumferential surface of the stator can then be exposedto the surrounding atmosphere, usually the surrounding air. Thus alsothe occurring heat can quickly and reliably be dissipated, withoutrequiring a forced guiding or a moving of the cooling air. As statedabove, a certain amount of heat is also led to the stator from thefrequency converter, which will cause the motor to get hot duringoperation. However, a balance between the heat admission and the heatdissipation occurs, so that the permitted temperatures are not exceeded.

Preferably, the frequency converter has a housing cover, which issubstantially adapted to the contour of the components of the frequencyconverter. This measure offers two advantages: Firstly, this embodimentrequires less sealing compound to fill the open volume in the frequencyconverter to prevent the components of the frequency converter fromgetting loose or damaged during operation due to vibrations. Secondly,the distances of heat transportation to the outside can be kept small.This provides an improved heat dissipation of the frequency converterand also secures that the frequency converter does not exceed thepermitted maximum temperatures.

Preferably, the frequency converter is connected with a temperaturesensor and/or a motor shaft angle sensor. The motor shaft angle sensoris practically obvious, as the bottom plate of the frequency convertercarries the bearing housing of the rotor. Mounting the frequencyconverter on the motor will thus provide that this sensor is already inthe correct position. The temperature sensor can also be arrangedwithout problems, as the frequency converter is immediately next to themotor. Thus, the temperature sensor can for example be arranged on thestator or on the stator winding.

Advantageously, the gear has a gear cover carrying a bearing housing fora gear shaft. This also provides that the gear, and thus the compactdrive, is kept compact.

It is also advantageous that the gear cover is made of aluminium oranother heat conductive metal. This provides that in a preferredembodiment the total gear housing is made of aluminium, so that on theone hand sufficient heat can be dissipated to the outside, and on theother hand the required stability is secured. Iron, stainless steel orsimilar materials can be used in stead of aluminium. In this embodimentthe gear housing cannot only dissipate heat produced in the gear. It canalso dissipate heat, led into the gear housing via the stator, from thefrequency converter to the surroundings.

Preferably, all bearing housings are open in the direction of the motor.This simplifies the fitting. For example, the frequency converter can befitted on one side of the motor and the gear without gear cover on theother side, the gear housing simply being fitted on the bearing of therotor. Finally, the gear is closed.

Advantageously, the compact drive is used as steering motor in avehicle. For this purpose, small dimensions and a low weight arenormally desired, and these conditions are met by the compact drive. Forexample, the compact drive can be used in a fork truck. The compactdrive then receives the required control signals from a steeringhandwheel or a joystick.

In the following the invention is described on the basis of a preferredembodiment in connection with the drawing, showing:

only FIGURE a schematic cross section through a compact drive.

A compact drive 1 has a motor 2 with a stator 3 and a rotor 4. Thestator 3 has a stator winding 5. The rotor 4 is rotatably arranged in astator bore 6 of the stator 3. The motor 2 is an a.c. motor or athree-phase motor.

On one front end, to the right in the FIGURE, a frequency converter 7 isarranged, which converts either a direct current into a one ormulti-phase alternating current or an alternating or three-phase currentwith a certain frequency into an alternating or three-phase current witha different frequency, with the purpose of supplying the motor 2.

On the other front end of the motor 2 a gear 8 is arranged, which has agear output shaft 9.

The frequency converter has a PCB 10 with the schematically shownelectrical components 11, 12, projecting at different lengths from thePCB 10. The PCB 10 is arranged in a chamber 13 limited by a bottom plate14 and a cover 15. Both the bottom plate 14 and the cover 15 areprovided with circumferential walls, enclosing the chamber 13 in theradial direction. The chamber 13 is filled with a sealing compound. Thissecures the components 11, 12 on the PCB 10 from loosening when the PCB10 is vibrating.

The cover 15 is made of injection-moulded plastic. The front end turningaway from the motor is not plane, but is substantially adapted to thecontour of the components. Thus, the cover 15 has a projection 16admitting the most projecting electrical component 12. As the cover 15is substantially adapted to the contour of the electrical components 11,12, the space 13 can be kept as small as possible, so that the requiredamount of sealing compound remains small. Additionally, this gives shortdistances between the electrical components 11, 12 and the surroundingair, which facilitates the heat dissipation.

On its side next to the stator, the bottom plate 14 has acircumferential wall 17, which again has a radially inside recess 18.The circumferential wall 17 is fitted on the stator 3 of the motor 2 ina way that the stator 3 extends into the recess 18. A correspondingadaptation of the size relations will cause that the stator is firmlyfixed in the bottom plate 14, which results in a heat conductingconnection in the area a. Heat produced by the frequency converter canthen on the one hand be transported direct to the surroundings, namelyvia the circumferential surface of the bottom plate 14, on the otherhand it can also be led into the stator 3, where a much larger heatdissipation surface is available.

Additionally, a bearing housing 19 is made on the bottom plate 14, inwhich a bearing 20 for the rotor 4 is arranged. In the bearing housing19 a motor shaft angle sensor 21 is provided, which is connected withelectrical components 11 on the platinum 10. In the stator a temperaturesensor 22 is provided, which is also connected with the frequencyconverter 7. Finally, an additional electrical connection 23, 24 can beseen between the stator winding 5 and the frequency converter 7. Anelectrical power can be supplied to the frequency converter 7 viaschematically shown receptacles 25, which can, for example, be mouldedtogether with the cover to obtain a tight connection.

On the opposite front end the gear 8 has a baseplate 26, which has, likethe bottom plate 14 of the frequency converter 7, a circumferential wall27 with a recess 28. The recess 28 is adapted to the stator 3 in a waythat the baseplate 26 can be mounted on the stator 3. Also here a heatconductive connection is obtained in the area b.

The baseplate 26 carries a bearing housing 29 for a bearing 30 of therotor 4. At the same time the bearing 30 also serves as bearing for agear shaft 31.

The inner construction of the gear 8 is merely shown schematically. Thegear can, for example, be a planetary gearing. Of course, other sorts ofgears are also possible. Being compact in relation to the obtainabletransmission, that is, having a large transmission at small volume, andbeing resistant to large overloads, a Cyclo-gear should be used. Thegear can also be replaced by a pump.

The gear inlet shaft 31 is also the rotor shaft, so that both gear 8 androtor 4 use the same bearing 30.

The individual parts of the gear 8 are arranged in a chamber 32 limitedon one side by the baseplate 26 and by a gear cover 33. Both gear cover33 and baseplate 26 have circumferential walls limiting the chamber 32in the radial direction.

A bearing housing 34 for a bearing 35 is provided in the gear cover 33,in which bearing the gear outlet shaft 9 is carried.

The gear cover 33 and the baseplate 26 are also made of aluminium. Theycan, for example, be made as casting or die casting members. The gear 8itself does not produce an excessive amount of heat. However, the gearhousing can then be used to emit heat, which is led to the motor 2 fromthe frequency converter via the stator 3, to the surroundings.

All bearing housings 34, 29, 19 open in the direction of the motor 2.This facilitates the assembly of the compact drive substantially. Forexample, the frequency converter 7 can be fitted on the stator 3 fromone side, and subsequently the rotor 4 can be inserted in the stator 3,so that it is carried in the frequency converter 7, or rather in thebottom plate 14. Then the gear 8 can be fitted from the other side.

Schematically shown is a bolt 36, which is stuck through the gear cover33 and the baseplate 26 and screwed into the bottom plate 14. Several ofsuch bolts, for example three, are provided evenly distributed in thecircumferential direction. By means of the bolts 36 the frequencyconverter 7 and the gear 8 are bolted together, thus clamping the motor2 between them. Further fixing opportunities for the motor 2 are notrequired, which makes additional working of the motor 2 in this respectsuperfluous.

In a way not shown, flanges can be heat conductively connected with thegear, particularly the gear cover, the frequency converter or thestator, which flanges can be used to fix the compact drive on a largerunit, for instance a vehicle or a machine. This will improve the heatdissipation even further.

What is claimed is:
 1. Compact drive comprising an electric motor, afrequency converter and a gear, the motor having opposite front ends,the frequency converter being located at one front end of the motor andthe gear being located at the other front end of the motor, the motor,frequency converter and gear being connected so that heat flows byconduction from the frequency converter to the motor and then to thegear.
 2. Compact drive according to claim 1, in which the frequencyconverter has a frequency converter housing with a bottom plate of aheat conductive material, the bottom plate being fitted on a stator ofthe motor.
 3. Compact drive according to claim 2, in which the bottomplate is in heat-conductive connection with the stator.
 4. Compact driveaccording to claim 2, in which the bottom plate has a bearing housingfor the rotor of the motor.
 5. Compact drive according to claim 4, inwhich the bottom plate has a circumferential centering projection in thearea of its circumferential edges next to the motor, which projectionsurrounds the stator.
 6. Compact drive according to claim 2, in whichthe bottom plate is made of aluminum.
 7. Compact drive according toclaim 2, in which the baseplate is made of aluminum.
 8. Compact driveaccording to claim 1, in which the gear has a baseplate of a heatconductive material, the baseplate being fitted on a stator of themotor.
 9. Compact drive according to claim 8, in which the baseplate isin heat-conductive connection with the stator.
 10. Compact driveaccording to claim 8, in which the baseplate has a bearing housing forthe rotor of the motor.
 11. Compact drive according to claim 10, inwhich the baseplate has a circumferential centering projection in thearea of its circumferential edges next to the motor, which projectionsurrounds the stator.
 12. Compact drive according to claim 1, in whichthe frequency converter and the gear are clamped together, holding themotor between them.
 13. Compact drive according to claim 1, in which thestator has a circumference in immediate connection with the surroundingatmosphere.
 14. Compact drive according to claim 1, in which thefrequency converter has a housing cover substantially conforming to thecontour of components of the frequency converter.
 15. Compact driveaccording to claim 1, in which the frequency converter is connected toat least one of a temperature sensor and a motor shaft angle sensor. 16.Compact drive according to claims 1, in which the gear has a gear covercarrying a bearing housing for a gear shaft.
 17. Compact drive accordingto claim 16, in which the gear cover is made of a heat conductive metal.18. Compact drive according to claim 1, in which that all bearinghousings are open in the direction of the motor.
 19. Compact driveaccording to claim 1, the compact drive being used as a steering motorin a vehicle.